Modulated Synthesis of Zr‐Based Metal–Organic Frameworks: From Nano to Single Crystals

TLDR

The study investigates how benzoic acid, acetic acid, and water modulate the synthesis of several Zr‑based metal‑organic frameworks (UiO‑66, UiO‑66‑NH₂, UiO‑67, UiO‑68‑NH₂). Crystal and particle size control was achieved and verified by powder XRD, SEM, DLS, and single‑crystal growth of Zr‑tpdc‑NH₂ enabled structural analysis. Adjusting modulator concentration altered crystal morphology from intergrown to individual crystals, tuned size, improved reproducibility of Zr‑bpdc, produced high‑surface‑area materials, and demonstrated that water is essential for well‑ordered Zr‑bdc‑NH₂.

Abstract

Abstract We present an investigation on the influence of benzoic acid, acetic acid, and water on the syntheses of the Zr‐based metal–organic frameworks Zr–bdc (UiO‐66), Zr–bdc–NH 2 (UiO‐66–NH 2 ), Zr–bpdc (UiO‐67), and Zr–tpdc–NH 2 (UiO‐68–NH 2 ) (H 2 bdc: terephthalic acid, H 2 bpdc: biphenyl‐4,4′‐dicarboxylic acid, H 2 tpdc: terphenyl‐4,4′′‐dicarboxylic acid). By varying the amount of benzoic or acetic acid, the synthesis of Zr–bdc can be modulated. With increasing concentration of the modulator, the products change from intergrown to individual crystals, the size of which can be tuned. Addition of benzoic acid also affects the size and morphology of Zr–bpdc and, additionally, makes the synthesis of Zr–bpdc highly reproducible. The control of crystal and particle size is proven by powder XRD, SEM and dynamic light scattering (DLS) measurements. Thermogravimetric analysis (TGA) and Ar sorption experiments show that the materials from modulated syntheses can be activated and that they exhibit high specific surface areas. Water proved to be essential for the formation of well‐ordered Zr–bdc–NH 2 . Zr–tpdc–NH 2 , a material with a structure analogous to that of Zr–bdc and Zr–bpdc, but with the longer, functionalized linker 2′‐amino‐1,1′:4′,1′′‐terphenyl‐4,4′′‐dicarboxylic acid, was obtained as single crystals. This allowed the first single‐crystal structural analysis of a Zr‐based metal–organic framework.